In the perfumery art, there is a considerable need for fragrant materials having fruity or flowery notes. Representative fragrant materials having fruity floral notes are such as δ-, α- and β-damascone. These damascone isomers have their own odor notes, respectively, while they have a fruity floral note basically. They are used differently according to their application purposes.
Damascones have three double-bond-depending isomers as described below.

A large number of production processes for these damascone isomers have been reported, for example, in “Review” (Shigeru Torii, et al., Koryo, No. 125, 47-60 (1979)). Among them, a production process of α-, β- and δ-damascone represented by the following reaction
wherein any one of dotted lines means a double bond.
The synthesis of α-, β- and δ-damascone involves two basic steps, namely, a Diels-Alder cycloaddition and an aldol condensation. The Diels-Alder cycloaddition produces 2,6,6-trimethylcyclohexenyl methyl ketone, from which damascones can be formed via further reaction steps, typically involving (a) epimerisation of cis- to trans-cycloadduct via enolate formation, (b) thermodynamic enolate addition to ethanal(acetaldehyde) to yield the corresponding aldol product and (c) dehydration of the aldol product to yield damascone.
2,6,6-Trimethylcyclohexenyl methyl ketone (1) is a useful compound as an intermediate for the synthesis of α-, β- and δ-damascone. It can be synthesized by a Diels-Alder reaction between 1,3-pentadiene and mesityl oxide as shown in the following reaction scheme:
Typically, more cis-cycloadduct than trans-cycloadduct is produced.
There is a need for new synthesis processes to improve the control of stereochemistry of the cycloadducts. There is also a need to have new synthesis processes to improve the yield of the desired damascone products.